a. Field of the Invention:
The present invention relates to a method for the preparation of a masterbatch composition being used for thermoplastic resin modification and having low tackiness and good workability.
More particularly, it relates to a method for the preparation of a masterbatch composition comprising polybutene and an ethylene.sup.. .alpha.-olefin copolymer obtained by copolymerizing ethylene with an .alpha.-olefin and having specific characteristics.
b. Description of the Prior Art:
A variety of molded articles, sheets and films are prepared from thermoplastic resins by molding processes such as injection molding, extrusion molding, blow molding and inflation molding. The thermoplastic resins are generally blended with various kinds of liquid, solid or powdery modifiers, for example, plasticizers, fillers, dyestuffs, pigments, lubricants, antioxidants and other agents in order to provide the resins with characteristics required for each application. These modifiers are blended with the thermoplastic resins in advance, pelletized and used. Alternatively, masterbatch pellets having a higher content of the modifiers are previously prepared and used for molding after dry blending with the base resin. Particularly in case of liquid modifiers, masterbatch pellets are generally prepared in advance and used after dry blending with the thermoplastic resins.
In case polybutene is used for the above modifiers, masterbatch pellets having a higher polybutene content must be prepared. Polybutene, however, causes the problems described below, because polybutene is poorly compatible with other polyolefin resins. Directly or several days after preparation, tackiness of the resulting pellets increases due to breeding of polybutene on the surface of the pellets.
Consequently, blocking of the pellets takes place with each other or bridging of the pellets occurs in a hopper in the dry blending operation. Accordingly, the prescribed amount of polybutene cannot be blended or ununiformity of the blended mixture is resulted even through blending procedures are performed. Thus blending operation becomes extremely difficult.